I don't believe that Morihei Ueshiba ever referred to his techniques as Ikkyo, Nikkyo etc. Correct me if I am wrong, but I believe that Kissomaru Ueshiba implemented most, if not all of the waza names, currently used within Aikikai circles. Also, I believe that the usage Ikkajo differs between Daito Ryu Aikijujutsu and Yoshinkan Aikido. While Ikkajo in Yoshinkan refers to the same technique as Ikkyo in Aikikai. In Daito Ryu, Ikkajo refers to a series of techniques. The specific waza which is analogous to Ikkyo in Aikikai, is referred to as Ippon Dori in Daito Ryu. There is an interview with the current head of Daito Ryu on Aikido Journal that explains this.

I second that 教 does not necessarily refer to religion. While it can refer to religious teachings, I believe that in this case it is just referring to teaching.